RF generator system for surgical vessel sealing

ABSTRACT

Systems, methods, and apparatus for providing power to an electrosurgical instrument. A method of providing power to an electrosurgical instrument includes generating a non-sinusoidal driving voltage having a substantially constant driving frequency; providing the non-sinusoidal driving voltage to a series LC circuit having a resonant frequency of substantially twice the substantially constant driving frequency and configured to present an impedance that limits current spikes and voltage transient spikes during load fluctuations; generating a quasi-sinusoidal current in the series LC circuit from the non-sinusoidal driving voltage; and providing the quasi-sinusoidal current to an electrical output, wherein the electrical output is configured for coupling to an electrical input of a bipolar tissue-sealing surgical instrument.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/704,587 filed May 5, 2015 and entitled “RF Generator System forSurgical Vessel Sealing,” which is a continuation of U.S. applicationSer. No. 13/277,979 filed Oct. 20, 2011 and entitled “RF GeneratorSystem for Surgical Vessel Sealing,” which claims priority to U.S.Provisional Application No. 61/405,761 filed Oct. 22, 2010 and entitled“RF Generator System for Surgical Vessel Sealing,” the entiredisclosures of which are hereby incorporated by reference for all properpurposes.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to surgical devices. Inparticular, but not by way of limitation, the present disclosure relatesto systems, methods and apparatuses for electrosurgically sealing bloodvessels.

BACKGROUND

Electrosurgical tools are used to permanently close vessels in minimallyinvasive surgical procedures. A combination of pressure and energyinitiates collagen melting and tissue fusion. This technology replacesall other hemostasis tools and provides fast and efficient vesselsealing. There are a number of tissue fusion energy devices approved inthe market for adult patients, however there is no similar single usedevice designed for small vessel applications and procedures.

Traditional vessel sealing devices can see sparking and dangerouscurrent spikes when there are short or open situations. Sparking andcurrent spikes result in part from the high currents used as well asenergy stored in LC circuits of traditional devices, where the LCcircuits are used to generate sinusoidal outputs provided to anelectrosurgical instrument. These LC circuits are also often driven attheir resonant frequency, which means they offer little impedance whenthe load impedance drops causing a current spike

Traditional vessel sealing devices also use large capacitors andinductors in LC circuits that store substantial energy, thus making itdifficult to quickly turn off such devices at the end of anelectrosurgical operation.

SUMMARY OF THE DISCLOSURE

Exemplary embodiments of the present invention that are shown in thedrawings are summarized below. These and other embodiments are morefully described in the Detailed Description section. It is to beunderstood, however, that there is no intention to limit the inventionto the forms described in this Summary of the Invention or in theDetailed Description. One skilled in the art can recognize that thereare numerous modifications, equivalents and alternative constructionsthat fall within the spirit and scope of the invention as expressed inthe claims.

In some aspects, a method of providing power to an electrosurgicalinstrument includes generating a non-sinusoidal driving voltage having asubstantially constant driving frequency; providing the non-sinusoidaldriving voltage to a series LC circuit having a resonant frequency ofsubstantially twice the substantially constant driving frequency andconfigured to present an impedance that limits current spikes andvoltage transient spikes during load fluctuations; generating aquasi-sinusoidal current in the series LC circuit from thenon-sinusoidal driving voltage; and providing the quasi-sinusoidalcurrent to an electrical output, wherein the electrical output isconfigured for coupling to an electrical input of a bipolartissue-sealing surgical instrument.

In some aspects, a power supply for an electrosurgical instrument isprovided. The power supply may have a power provider configured toprovide a non-sinusoidal voltage at a substantially constant drivingfrequency and a variable amplitude; a series LC circuit configured toreceive the non-sinusoidal voltage and provide a quasi-sinusoidalcurrent, and wherein the resonant frequency of the series LC circuit issubstantially twice that of the substantially constant drivingfrequency; and an electrical output configured to provide thequasi-sinusoidal current to a bipolar tissue-sealing electrosurgicalinstrument; wherein the electrical output has a maximum voltage of about75 Volts, and a maximum current of about 1.8 amperes.

BRIEF DESCRIPTION OF THE DRAWINGS

Various objects and advantages and a more complete understanding of thepresent invention are apparent and more readily appreciated by referringto the following detailed description and to the appended claims whentaken in conjunction with the accompanying drawings:

FIG. 1 illustrates a power supply for providing power to anelectrosurgical instrument.

FIG. 2 illustrates another embodiment of a power supply for providingpower to an electrosurgical instrument.

FIGS. 3A-3F illustrate six alternative arrangements of an inductor andcapacitor in the LC series circuit.

FIG. 4 illustrates current output from one or more of the LC circuitsdescribed herein for low load impedances.

FIG. 5 illustrates current output from one or more of the LC circuitsdescribed herein for high load impedances.

FIG. 6 illustrates a method of providing power to an electrosurgicalinstrument.

FIG. 7 shows a diagrammatic representation of one embodiment of amachine in the exemplary form of a computer system within which a set ofinstructions for causing a device to perform any one or more of theaspects and/or methodologies of the present disclosure to be executed.

DETAILED DESCRIPTION

FIG. 1 illustrates a power supply for an electrosurgical instrument. Thepower supply 100 can include a power provider 102, an LC circuit 108,and an electrical output 110, and the power supply 100 can be configuredto couple to and provide power to an electrosurgical instrument 114. Thepower provider 102 can provide a non-sinusoidal voltage (e.g., pulsed DCvoltage or a square wave having finite switching time) to the LC circuit108 (e.g., capacitor and inductor in series). The non-sinusoidal voltagecan have a constant, or substantially constant (e.g., plus or minus 50ppm (0.005%)), drive frequency and a variable amplitude.

The LC circuit 108 can receive the non-sinusoidal voltage and convertthe voltage to a quasi-sinusoidal current. The non-sinusoidal voltage,or driving voltage, can operate at substantially half a resonantfrequency of the LC circuit 108. Exemplary constant drive frequenciescan include the range 225 to 275 KHz, with a plus or minus 50 ppm jitterfor any constant drive frequency in that range, where the jitter isinherent to the electronics (e.g., a crystal oscillator).

The constant drive frequency can be initially tuned to one half the LCcircuit 108 resonance and parasitic inductances and capacitances, butdoes not change from one surgical operation to the next (further tuningis possible but not required). In some embodiments, while the resonantfrequency of the LC circuit 108 is typically beyond control (assumingfixed capacitors and inductors and neglecting changes in capacitance andinductance for different cables 112), the constant drive frequency ofthe pulse generator 106 can be tuned to align with the resonance of theLC circuit 108 (e.g., where constant drive frequency is substantiallyhalf the resonant frequency). By operating at substantially half theresonant frequency of the LC circuit 108, the LC circuit 108 presents animpedance to current passing through the LC circuit 108 (thequasi-sinusoidal current) as compared to the negligible or substantiallynegligible impedance that would be seen were the LC circuit 108 drivenat or near its resonant frequency.

The quasi-sinusoidal current (e.g., see 404, and 504 in FIGS. 4-5) canbe provided to an electrical output 110. The electrical output 110 canbe configured for coupling to and providing the quasi-sinusoidal currentto an electrosurgical instrument 114 (e.g., a bipolar instrument) via acable 112. The quasi-sinusoidal current varies depending on loadimpedance. At lower load impedances (e.g., 6-25Ω), the quasi-sinusoidalcurrent resembles the damped ringing output of an LC circuit with apolarity flip (or 180° phase shift) every cycle. For example, see thecurrent 404 illustrated in FIG. 4. As load impedance increases (e.g., asa vessel is heated during electrosurgical sealing), the quasi-sinusoidalcurrent begins to resemble the driving signal (e.g., pulsed waveform)(e.g., at 75-256Ω). An exemplary quasi-sinusoidal current for suchhigher impedances can be seen in FIG. 5.

Although a constant drive frequency will be hereinafter referred to, itis to be understood that a substantially constant drive frequency isalso intended. The range of constant drive frequencies included is225-275 KHz and for a targeted constant drive frequency, the electronicsmay have a frequency stability or jitter of plus or minus 50 ppm. Also,although absolute multiples of frequencies (e.g., twice and three timesand four times) will be hereinafter referred to, it will be clear to oneof skill in the art that multiplies of frequencies can include adjacentfrequencies of plus or minus 25 KHz (e.g., 225-275 KHz given a constantfrequency of 250 KHz).

In an embodiment, the power provider 102 can include a power source 104and a pulse generator 106 connected via a DC bus 105. The power source104 can provide DC power (positive current) at a variable amplitude tothe pulse generator 106 via the DC bus 105. The power source 104 canalso receive DC power (negative current) at from the pulse generator106. The pulse generator 106 can receive the variable amplitude DC powerand convert it to pulsed voltage having a constant drive frequency andhaving an amplitude dependent upon the variable amplitude received fromthe power source 104.

The power provider 102 and/or the included power source 104 can operatein a constant power mode. Constant power means that the voltage and/orcurrent are automatically adjusted to maintain a desired or set poweroutput (to within a margin of error of +/−20%). For instance, as theload impedance increases current decreases, and the voltage output ofthe power provider 102 increases to offset the current decrease and thusmaintain constant power. In another example, as the load impedancefalls, the current rises, and the voltage of the power provider 102decreases to maintain constant power output. Thus, for constant powerset to 5 W, constant power may include 4-6 W. For constant power set to10 W, constant power may include 8-12 W. For constant power set to 15 W,constant power may include 12-18 W. The constant power may include therange 0-20 W, 2-15 W, 5-10 W, 10-14 W, or 5-12 W, to name just a fewnon-limiting examples. Load impedance is primarily that of the tissuebeing operated upon by the electrosurgical instrument 214, for instancewhen grasped between tines of an electrosurgical surgical instrument.

In one embodiment, the power source 104 includes a power converter(e.g., buck-boost converter) capable of upconverting or downconvertingcurrent and/or voltage. The power converter can have a controllableamplitude that can be controlled, for instance, via a feedback loop thatdetects and analyzes one or more of current, voltage, power, andimpedance at or near the electrical output 110. The power converter canbe of a type configured to both source and absorb current. For instance,one or more capacitors of the power converter can absorb energy ifneeded and later provide that energy back to the LC circuit 108. Theability to absorb energy enables the LC circuit 108 to periodically(e.g., during a time period of each pulse of the quasi-sinusoidalcurrent) discharge some or all stored energy back into the DC bus 105and thus accumulate little to no stored energy. This enables less severesparking and current spiking than traditional power supplies.

Current spikes occur when the load impedance drops quickly and theenergy stored in the LC components flows into the load. The energyavailable for such a current spike is traditionally larger than desiredsince energy builds up in an LC circuit. Moreover, the current can risequickly since traditional LC circuits are driven at or near resonance,where the LC circuit has little or negligible impedance. However, here,where energy is discharged during a period of time every cycle of the LCcircuit 108, only the energy stored during a single cycle is availablefor discharge during a short circuit condition, and thus current spikesand sparking are less severe than in the prior art. The severity ofthese events is also mitigated by the fact that the LC circuit 108 isdriven at other than the resonant frequency (e.g., half the resonantfrequency). The result is that the LC circuit 108 acts as an impedanceto the driving signal and thus limits changes in current as well asabsolute current during a current spike.

An additional advantage of not accumulating energy in the LC circuit isthat power can be shut off to the electrosurgical device in a shorteramount of time, thus giving surgeons greater control over the surgicalendpoint. Additionally, the use of smaller inductors and capacitors inthe LC circuit than is done in the art, also shortens the cutoff time.

In comparison, were switching to occur at the resonant frequency of theLC circuit 108, the LC circuit 108 would present 0 or negligibleimpedance to the current. The result would be more sever current spikesand sparking and the inability to discharge substantially all energy inthe LC circuit 108 back to the DC bus 105.

In one embodiment, the pulse generator 106 is an h-bridge. The h-bridgemay receive DC power from the power source 104 and output pulsed voltage(e.g., square wave) to the LC circuit 108. The pulsed voltage can beprovided at a constant drive frequency that is based on characteristicsof the LC circuit 108 (e.g., the resonant frequency of the LC circuit108). For instance, a substantially constant drive frequency can be setto be substantially one half a resonant frequency of the LC circuit 108.In other words, the drive pulses can alternate polarity ever other cycleof the LC circuit 108 when the LC circuit 108 is driven such that itrings at its resonant frequency. An amplitude of the pulsed power can bedictated by the amplitude of DC power provided by the power source 104.The h-bridge can source and absorb current, which like the powersource's 104 ability to source and absorb, enables the LC circuit 108 todischarge energy back to the DC bus 105 during a period of time once percycle. Such a period of time can include the second half of each pulseof the driving voltage, which preferably correlates to the second halfof each period of the quasi-sinusoidal current.

To discharge energy back into the DC bus 105, the driving voltage'spolarity can be switched 180° out of phase with a zero crossing of thequasi-sinusoidal current and at a frequency substantially equal to onehalf the resonant frequency (for low impedance). Operated as such, theLC circuit 108 presents a substantial impedance to current thuspresenting an upper limit to current spikes and mitigating the rise incurrent during a current spike. Also, instead of enabling energy tobuild and accumulate in the LC circuit 108, stored energy dischargesback to the DC bus 105 during one half of each resonant cycle.

For instance, at low load impedance (e.g., 6-26Ω) during the first halfof positive and negative voltage pulses from the pulse generator 106,energy passes from the DC bus 105 to the LC circuit 108 and theelectrosurgical instrument 114. The DC bus 105 sees positive current andthe driving voltage and quasi-sinusoidal current have the same polarity.During the second half of voltage pulses, energy passes from the LCcircuit 108 back to the DC bus 105 where it can be stored and thenresupplied to the LC circuit 108 and the electrosurgical instrument 114during the first half of the next voltage pulse. The DC bus 105 seesnegative current and the driving voltage and quasi-sinusoidal currenthave opposite polarity during this time when energy is returned to theDC bus 105.

The LC circuit 108 can include an inductive component (e.g., aninductor) and a capacitive component (e.g., a capacitor) in series.Various configurations of the inductive and capacitive components in theLC circuit 108 can be seen in FIG. 3.

In order to decrease switching losses, pulses can be switchedsubstantially at a minimum current in the LC circuit 108 or when currentapproaches 0 amperes. This is typically possible at low impedance wherecurrent crosses 0 amperes once per resonant cycle of the LC circuit 108and approaches 0 amperes once per resonant cycle of the LC circuit 108(see FIG. 4). Switching is preferable, not at the 0 crossing, but at ornear to where the quasi-sinusoidal current approaches 0 amperes. Athigher impedance, the quasi-sinusoidal current does not approach 0amperes to the same extent as at low impedance (see FIG. 5), and thusswitching losses are more difficult to avoid.

Voltage pulses may have finite switching times, in which case thephasing of the pulsed voltage is selected such that either thebeginning, end, or some middle portion of the finite switching timeperiod occurs at the same moment that the quasi-sinusoidal current inthe LC circuit 108 approaches 0 amperes (for low impedance).

The LC circuit 108 can be driven at half its resonant frequency, anddriven via pulsed or square waves voltages (or some other non-sinusoidaldriving waveform). Phasing of the driving voltage pulses may be timed tooccur substantially at the moment that the quasi-sinusoidal current inthe LC circuit 108 approaches 0 amperes (at low impedance). This uniquedriving frequency and phasing along with use of a power provider 102that can source and absorb energy enables the LC circuit 108 todischarge energy back to the power provider 102 during a part of eachcycle and thus decrease energy stored in the LC circuit 108. In oneembodiment, during pulse transitions, the LC circuit 108 dischargessubstantially all energy stored therein back to the power provider 102.

FIG. 2 illustrates another embodiment of a power supply for providingpower to an electrosurgical instrument. The power supply 200 includes apower source 204, a pulse generator 206 (e.g., an h-bridge), and an LCcircuit 208. The power source 204 can include a source 222, and a powerconverter (e.g., buck-boost converter 220) and be coupled to the pulsegenerator 206 via a DC bus 205. The LC circuit 218 can include one ormore inductive elements (e.g., inductor 242), one or more capacitiveelements (e.g., capacitor 240), and a transformer 246. The power supply200 is also configured to be coupled to a cable 212 via electricaloutput 210, and the cable 212 can be coupled to an electrosurgicalinstrument 214 (e.g., a bipolar instrument). The power supply 200 canalso include one or more sensors 250 for monitoring various electricalcharacteristics (e.g., voltage, current, power, impedance) at or nearthe electrical output 210. The one or more sensors 250 can providefeedback signals to a feedback controller 260 configured to control, orprovide instructions for controlling, an amplitude of DC power generatedby the power source 204. An optional frequency controller 270 cancontrol a frequency of pulses from the pulse generator 206, and can becontrolled via feedback, or can be controlled from a memory (e.g.,solid-state memory or disk drive memory) or user input.

The power source 204 can include a power converter such as buck-boost220 which can upconvert and/or downconvert power from source 222. Thebuck-boost generates DC power having a variable or controllableamplitude, where the amplitude is controlled by the feedback controller260. The amplitude of the DC power can depend on various limits such asa current and voltage limit. Current and voltage limits may exist toprotect against short and open circuit anomalies. These limits not onlyprovide safety to the surgeon and the patient, but also preventunexpected electrical phenomena.

In an embodiment, the one or more sensors 250 provide feedback regardingcurrent and voltage at or near the electrical output 210. The feedbackcontroller 260 compares the measured current and/or voltage to currentand/or voltage limits or thresholds (e.g., a voltage maximum at 75 voltsand a current range of between 1.3 and 1.8 amperes). If the measuredcurrent or voltage exceeds a limit or threshold, then the feedbackcontroller 260 can instruct or signal the power source 204 (or thebuck-boost 220 of the power source 204) to decrease current and/orvoltage.

This decrease can be predetermined (e.g., cutting current by 50%) or canbe based on real-time measurements of current and/or voltage. Forinstance, the current may be decreased until the current or voltage,whichever exceeded a limit, falls below the limit. The rate of decreasemay be based on real-time measurements of current, voltage, power, andimpedance from the one or more sensors 250. For instance, where currentor voltage are observed to exceed the threshold by a certain percentageor are exceeding the threshold at a certain rate, the decrease involtage may be more severe than if the voltage or current exceeded thethreshold or the rate of voltage or current increase were not as great.

There may also be a power limit as defined by a power profile that maybe selected based on a desired power profile (e.g., a symmetric ornon-symmetric trapezoid) to be applied to tissue during a sealingoperation. The one or more sensors 250 can monitor power and provideinformation regarding the power to the feedback controller 260. Thefeedback controller 260 can compare the monitored power to a powerprofile (e.g., stored in a memory) and instruct or signal the powersource 204 (or the buck-boost 220 of the power source 204) to decreasepower should the monitored power exceed the power profile. Thebuck-boost 220 may have a tendency to increase power towards the highestcurrent or voltage provided by the source 222, such that the buck-boost220 provides the highest power possible that does not exceed thethresholds or limits set by the feedback controller 260.

However, it should be noted that the power source 204 and the buck-boost220 of the power source 204 preferably provide constant power to the DCbus 205. In other words, rather than the power source 204 or buck-boost220 being a current source (constant current, variable voltage) or avoltage source (constant voltage, variable current), they may havevariable current and voltage so as to achieve a constant power output.The advantage of an inherent constant power source is that there is nota critical demand on the feedback circuit to indirectly control power byeither controlling voltage or current. This makes the control circuitmore reliable and can eliminate transient spikes that may otherwiseoccur with conventional voltage or current sources.

In one embodiment, the feedback controller 260 controls a switch (e.g.,FET) that couples an inductor across output terminals of the source 222.In this state, inductor current rises linearly with time until reachinga current threshold. The current threshold can be based upon feedbackfrom the one or more sensors 250. Once the current reaches the currentthreshold, the power source 204 provides constant power since any changein impedance results in the power source 204 providing different currentand voltage yet maintaining the same power output. The current andvoltage of the power source 204 vary automatically as a result ofimpedance changes, but also due to changes in the constant power outputas controlled by the feedback controller 260.

By critical demand on the feedback it is meant that there is a limit tohow quickly feedback systems can operate before they become unstable(e.g., faster response leads to greater instability until, at a criticalresponse time, the system becomes unstable).

The power source 204 and the buck-boost 220 are also capable of sourcingand absorbing current (voltage rises when current is absorbed). Thischaracteristic is not common to all power sources, and here providesunique advantage since it aids in preventing buildup of energy in the LCcircuit 208 by allowing the LC circuit 208 to return energy to the DCbus 205. In other words, power sources incapable of sourcing andabsorbing current may not be capable of achieving the current spike andspark mitigation or rapid cutoff that the power supply 200 is capableof. For instance, the power source 204 may include a buck-boost having acapacitor bank (not illustrated) able to absorb current and thenresupply the absorbed current to the LC circuit 208. The absorbedcurrent can be resupplied to the LC circuit 208 in a next resonant cycleof the LC circuit 208.

The pulse generator 206 produces a non-sinusoidal voltage, such aspulsed or square waves. It can also take the form of an h-bridge or anyother switched mode power supply, and can produce pulsed or square wavesignals. The h-bridge can comprise four field effect transistors (FET)in one embodiment, and the four FETs can diagonally switch on and off tocreate pulsed power or square waves that alternate the polarity of powerbeing applied to the LC circuit 208. FETs are chosen that minimize orreduce losses. The pulse generator 206 is capable of sourcing andabsorbing current, which, like the power source 204, enables the uniquecurrent spike and spark prevention along with rapid cutoff of the powersupply 200. The pulse generator 206 produces pulses at a constant drivefrequency (e.g., 250 KHz+/−25 KHz or any frequency less than 500 KHz) asdictated by the optional frequency controller 270 and at a variableamplitude where the amplitude is controlled by the DC power provided bythe power source 204. In one embodiment, the pulse generator 206generates a constant driving frequency at 240 KHz with perhaps a +/−5ppm jitter.

During a surgical operation, the constant driving frequency (frequencyof the pulses) is kept constant while amplitude of the voltage pulsescan be adjusted via the power source 204. Changes in amplitude of thepulses affect the shape of the quasi-sinusoidal current of the LCcircuit 208 (along with load impedance) and thus the average powerdelivered to the electrosurgical instrument 214. Thus, changes inamplitude of the voltage pulses can be used to track a power profilethat is to be applied during a surgical operation (e.g., vesselsealing). The amplitude of DC current and voltage provided by the powersource 204 automatically adjusts when the load impedance changes(impedance of the electrosurgical surgical instrument 214) since thebuck-boost 220 outputs constant power (for a given set point of thepower profile).

Although the switching is described as pulsed or square wave in nature,in practice the ‘pulses’ can have a trapezoidal shape. In other words,switching time from one pulse to the next is finite. Furthermore,although the circuitry of the power supply enables nearly instantaneousswitching (or a pure square wave), this maximum performance of thecircuitry may not always be utilized and thus switching may involve aslight ramping up or down in voltage and/or current rather than adiscrete jump. Since switching time is finite, the constant drivefrequency can be tailored so that the transition between pulses occurssubstantially at or near a time when the quasi-sinusoidal current in theLC circuit 208 approaches 0 amperes (at low impedance). In oneembodiment, the start of a transition between pulses occurssubstantially at the same time as the quasi-sinusoidal current in the LCcircuit 208 approaches 0 amperes.

In some embodiments, the optional frequency controller 270 can instructor signal the pulse generator 206 to provide pulsed voltage to the LCcircuit 208 at a constant drive frequency. By constant, it is meant thatduring a given tissue operation or vessel sealing operation thefrequency of pulses delivered to the LC circuit 208 is constant. Inother embodiments, the constant driving frequency can be adjustedbetween operations in order to tune the constant driving frequency tothe resonance of the LC circuit 208 (e.g., half the resonant frequencyof the LC circuit 208). The resonant frequency of the LC circuit 208 candepend on the inductive (e.g., inductor 242) and capacitive (e.g., 240)elements or components of the LC circuit 208 as well as parasitics(e.g., in a transformer of the LC circuit 208 as well as the cable 212,which is not technically part of the LC circuit 208).

Although not illustrated as having a feedback mechanism, in alternativeembodiments, the optional frequency controller 270 can receive feedbacksignals from the LC circuit 208 indicating electrical characteristics ofthe LC circuit 208 (e.g., voltage, current, power, load impedance, LCcircuit impedance, impedance or reactance of the capacitor 240 orinductor 242, impedance or reactance of parasitic from the transformer246 and cable 212).

The LC circuit 208 can include one or more capacitive elements (e.g.,capacitor 240), one or more inductive elements (e.g., inductor 242), anda transformer 246. The capacitor 240 and inductor 242 can be arranged inseries (variations of this arrangement can be seen in FIG. 3). Thetransformer 246 can also be arranged between the two conductive lines orwires of the LC circuit 208 to provide electrical isolation between theelectrosurgical instrument 214 and the rest of the power supply 200. Thetransformer 246 can have a 1:4 turns ration (primary:secondary) and bewound around a magnetic core using conductive wire having a diameterselected to minimize skin effects (e.g., thin diameter wire). In oneembodiment, leakage inductance from the transformer 246 is on the orderof no more than 5 μH.

The capacitor 240 can be selected to have a lower capacitance thantraditional capacitors used in this capacity, so that less charge isstored in the LC circuit 208. Lower energy being stored in the LCcircuit 208 means there is less energy available for discharge into theelectrosurgical instrument 214 in the event of a short or open. Lowerstored energy means that power can be cutoff faster than in devicesusing larger inductive and capacitive components. In particular,exemplary capacitance values for the capacitor 240 include, but are notlimited to, 0.01-1.0 μF.

The inductor 242 can be a discrete inductor. However, when determiningthe constant drive frequency of the pulsed voltage provided by the pulsegenerator 206, the inductance of the LC circuit 208 can be considered toinclude the value of the discrete inductor 242 as well as parasiticinductances from the transformer 246 and the cable 212, and even theelectrosurgical instrument 214. In other words, the resonant frequencyof the LC circuit 208 that the pulse generator 206 is tuned to, takesinto account parasitic effects and even parasitic effects of the cable212 and instrument 214 outside of the LC circuit 208.

The capacitor 240 can be discrete, and like the inductance, thecapacitance used to determine the LC circuit 208 resonant frequency candepend on the discrete capacitor 240 capacitance as well as parasiticcapacitances inside and outside of the LC circuit 208.

In one embodiment, the inductive circuit comprises two or more inductiveelements coupled to each other in series or in parallel. The capacitivecircuit can comprise two or more capacitive elements coupled to eachother in series or in parallel.

The one or more sensors 250 can include a current and voltage sensor.There can also be a power sensor, or the signals from the current andvoltage sensors can be used to calculate the power (e.g., voltage timesamplitude). There can also be an impedance sensor that measures the loadimpedance as well as the LC circuit 208 impedance, or these impedancescan be calculated based on the current and voltage measured by thecurrent and voltage sensors. Measurements can be taken at or near theoutput 210. In one embodiment, the one or more sensors 250 can beisolated from the electrosurgical instrument 214, for instance via useof a transformer (not illustrated).

In one embodiment, the inductor 242 and capacitor 240 can be adjusted(e.g., either mechanically or electrically) to change the impedance andreactance of the LC circuit 208 and hence the resonant frequency inorder to adapt to changes in the cable 212, electrosurgical instrument214, and/or the tissue being operated on. For instance, the inductanceand capacitance could be electrically altered to account for differentelectrosurgical instruments 214 being coupled to the power supply 200.

This power supply 200 is advantageous because it inherently produces adesired operation in which at low load impedance the power supply 200provides high current to the tissue, while at high load impedance (assealing nears completion) it provides high voltage. In particular, useof a constant power source such as power source 204 inherently producesthese electrical characteristics that are not achieved when a current orvoltage source are used. For instance, since constant power is beingused, the ratio of voltage over current equals impedance. So, as loadrises, the ratio of voltage to current increases.

FIGS. 3A-3F illustrate six alternative arrangements of the inductor 242and capacitor 240 in the LC circuit 208. Each of these configurationsfall within this disclosure's definition of an LC circuit (e.g., LCcircuit 208) with an inductor and capacitor in series—a series LCcircuit. Each of the illustrated configurations could be substitutedinto FIG. 2 for the LC circuit 208 (FIG. 3A is identical to LC circuit208 in FIG. 2), where the pulse generator 206 is to the left of FIG. 3and the electrical output 210 is to the right.

FIG. 4 illustrates current in one or more of the LC circuits describedherein for low load impedances. Such low load impedances may be seen atthe start and early portions of a surgical operation such as vesselsealing. The LC circuit can take the form of those illustrated in FIGS.1-2 (e.g., 108, 208). Since the LC circuit 108, 208 is a series circuit,the current 404 entering the LC circuit 108, 208, inside the LC circuit108, 208, and leaving the LC circuit 108, 208 are the same. Similarly,the current 404 between the pulse generator (e.g., 106, 206) and the LCcircuit 108, 208 and that provided to the electrosurgical instrument(e.g., 114, 214) is also represented by the current 404 of FIG. 4. Lowimpedance can include, but is not limited to, a load impedance of 6-25Ω.

A driving voltage 402 from the pulse generator 106, 206 to the LCcircuit 108, 208, herein illustrated as a square wave (although othernon-sinusoidal waveforms are also envisioned), is switched at half aresonant frequency of the LC circuit 108, 208. The current 404 is inphase with the driving voltage 402 and sees a 180° phase shift onceevery current 404 cycle, and twice every cycle of the driving voltage402. The 180° phase shift, or polarity reversal, occurs at approximately96 μs, 98 μs, 100 μs, 102 μs, and 104 μs.

It should be noted that the values of time and current for the waveformsin FIG. 4 were arbitrarily generated, and thus are not meant to limitthe scope of the disclosure. The driving voltage 402 is illustrated withan arbitrary voltage and is not necessarily drawn to scale relative tothe current 404.

As seen, the current 404 resembles a dampened sine wave that sees a 180°phase shift or polarity reversal each time the driving voltage 402 fromthe pulse generator 106, 206 switches. Current 404 crosses 0 amperesnear 97 μs, 99 μs, 101 μs, and 103 μs. Current approaches 0 amperes ator near 96 μs, 98 μs, 100 μs, 102 μs, and 104 μs. Although asillustrated, the current 404 does not reach 0 amperes when the drivingvoltage 402 switches, in other embodiments, the circuitry used is suchthat the current reaches 0 amperes when the driving voltage 402switches.

The DC bus (e.g., 105, 205) provides energy to the LC circuit 108, 208and the electrosurgical instrument 114, 214 whenever the driving voltage402 and current 404 have the same polarity. For instance, energy isprovided to the LC circuit 108, 208 and the electrosurgical instrument114, 214 during the time periods between: 96-97 μs, 98-99 μs, 100-101μs, 102-103 μs and 104-105 μs. During these time periods, current in theDC bus 105, 205 is positive. Energy is returned to the DC bus 105, 205and discharged from the LC circuit 108, 208 whenever the driving voltage402 and current 404 have opposite polarity. For instance, energy isreturned to the DC bus 105, 205 and discharged from the LC circuit 108,208 during the time periods between: 95-96 μs, 97-98 μs, 99-100 μs,101-102 μs, 103-104 μs.

Thus, the DC bus 105, 205 provides current and energy during the firsthalf of each driving voltage 402 pulse from the pulse generator 106,206, and absorbs current and energy during the second half of eachdriving voltage 402 pulse. As a result, at or near the pulse switching,substantially all energy stored in the LC circuit 108, 208 will havebeen discharged back to the DC bus 105, 205. Hence, at the start of eachdriving voltage 402 pulse, the LC circuit 108, 208 is substantiallydevoid of stored energy. This should be compared to a typical LCcircuit, where the inductor and capacitor alternately store asubstantial amount of energy throughout an LC circuit cycle.

FIG. 5 illustrates current output in one or more of the LC circuitsdescribed herein for high load impedances. Such high load impedances maybe seen near the end or latter portions of a surgical operation such asvessel sealing. The LC circuit can take the form of those illustrated inFIGS. 1-2 (e.g., 108, 208). High impedance can include, but is notlimited to, a load impedance of 75-256Ω.

A driving voltage 502 from the pulse generator 106, 206 to the LCcircuit 108, 208, herein illustrated as a square wave (although othernon-sinusoidal waveforms are also envisioned), is switched at half aresonant frequency of the LC circuit 108, 208. The current 504 is inphase with the driving voltage 502 and sees a 180° phase shift onceevery current 504 cycle, and twice every cycle of the driving voltage502. The 180° phase shift, or polarity reversal, occurs at approximately10 μs, 12 μs, 14 μs, 16 μs, and 18 μs.

It should be noted that the values of time and current for the waveformsin FIG. 5 were arbitrarily generated, and thus are not meant to limitthe scope of the disclosure. The driving voltage 502 is illustrated withan arbitrary voltage and is not necessarily drawn to scale relative tothe current 504.

Unlike the current 404 for low impedance, at high impedance, ringing inthe LC circuit 108, 208 is sufficiently damped that the sinusoidal shapeof the current 404 seen in FIG. 4 is not visible in FIG. 5. Rather, thecurrent 504 more closely resembles the pulsed driving voltage 502 thatswitches at or near approximately 10 μs, 12 μs, 14 μs, 16 μs, and 18 μs.In other words, switching occurs at or near a point where the current504 crosses 0 amperes. Also, unlike the low impedance situationillustrated in FIG. 4, at higher impedance, energy is only provided fromthe DC bus 105, 205 to the LC circuit 108, 208 and the electrosurgicalinstrument 114, 214. As seen, the current 504, and driving voltage 502,are always of the same polarity, and thus energy is not returned to theDC bus 105, 205.

FIG. 6 illustrates a method of providing power to an electrosurgicalinstrument. The method 600 involves first generating a non-sinusoidaldriving voltage having a constant driving frequency in a first generateoperation 602. The method 600 further includes providing thenon-sinusoidal driving voltage to an LC circuit having a resonantfrequency twice the driving frequency in the first provide operation604. The method also generates a quasi-sinusoidal current from thenon-sinusoidal driving voltage in a second generate operation 606.Finally, the method 100 provides the quasi-sinusoidal current to anelectrical output in a second provide operation 608. In the secondprovide operation 608, the electrical output is configured for couplingto an electrical input of a surgical instrument.

The generate operation 602 can be carried out, for instance, via a powerprovider 102 (see FIG. 1), or the combination of a power source 204 anda pulse generator 206 (see FIG. 2). The non-sinusoidal driving voltagecan be a pulsed waveform such as a square wave, where the waveform canbe shaped via an h-bridge of the pulse generator 206 that receives DCpower from a power source 204 that can include a buck-boost converter220. The constant driving frequency can be controlled via a controllersuch as the optional frequency controller 270.

The first provide operation 604 can provide the non-sinusoidal drivingvoltage to an LC circuit (e.g., LC circuit 208). The non-sinusoidaldriving voltage can be tuned, prior to a surgical operation (e.g.,during manufacturing, or during periodic technician tune-ups), to afrequency equivalent to one half of a resonant frequency of the LCcircuit (e.g., one half the resonant frequency). By driving the LCcircuit at half its resonant frequency, the LC circuit presents animpedance to the driving signal and current passing through the LCcircuit that mitigates current spikes and sparking. Driving the LCcircuit at half its resonant frequency also enables the LC circuit todischarge energy stored therein every resonant cycle back to the powersource (e.g., power source 204), thus leaving less stored energyavailable for current spikes and sparking. The lower level of storedenergy also enables faster cutoff times when a surgical operation ends.Also, current spikes and sparking are less severe than in the art sincethe LC circuit impedance limits current changes and creates an upperlimit on current.

The resonant frequency can be determined based on capacitance andinductance of discrete capacitive and inductive devices in the LCcircuit (e.g., of capacitor 240 and inductor 242) as well on parasiticcapacitance and inductance (e.g., of transformer 246 and cable 212).

The second generate operation 606 generates a quasi-sinusoidal currentusing a circuit such as LC circuit 208. For instance, in the LC circuit208, a pulsed voltage may be converted to the quasi-sinusoidal currentsillustrated in FIGS. 4-5. The quasi-sinusoidal current can be providedto an electrical output such as output 110, 210 in the second provideoperation 608. The electrical output can be configured for coupling to acable (e.g., cable 212) and the cable can couple to a surgicalinstrument (e.g., surgical instrument 214).

The systems and methods described herein can be implemented in a machinesuch as a computer system in addition to the specific physical devicesdescribed herein. FIG. 7 shows a diagrammatic representation of oneembodiment of a machine in the exemplary form of a computer system 700within which a set of instructions for causing a device to perform anyone or more of the aspects and/or methodologies of the presentdisclosure to be executed. Computer system 700 includes a processor 705(or CPU) and a memory 740 that communicate with each other, and withother components, via a bus 755. For instance, the feedback controller260 and/or the optional frequency controller 270 can include a processorsuch as processor 705. Bus 755 may include any of several types of busstructures including, but not limited to, a memory bus, a memorycontroller, a peripheral bus, a local bus, and any combinations thereof,using any of a variety of bus architectures.

Memory 740 may include various components (e.g., machine readable media)including, but not limited to, a random access memory component (e.g., astatic RAM “SRAM”, a dynamic RAM “DRAM”, EEPROM, etc.), a read onlycomponent, and any combinations thereof. In one example, a basicinput/output system 742 (BIOS), including basic routines that help totransfer information between elements within computer system 700, suchas during start-up, may be stored in memory 740. Memory 740 may alsoinclude (e.g., stored on one or more machine-readable media)instructions or code (e.g., software) 746 embodying any one or more ofthe aspects and/or methodologies of the present disclosure. In anotherexample, memory 740 may further include any number of program modulesincluding, but not limited to, an operating system 744, one or moreapplication programs 746, other program modules 746, program data 746,and any combinations thereof. For instance, the memory 740 can storedata describing a desired power profile to be used by a controller, suchas feedback controller 260 (see FIG. 2) to control a power source, suchas power source 204. The memory 740 may also include data describingsettings for the constant drive frequency and variable amplitude as afunction of the type of electrosurgical instrument 214 being used withthe power supply 200. The memory 740 may also contain voltage, current,and power thresholds that the feedback controller 260 can use tomitigate voltage and current spikes as well as to help the power track apower profile.

Computer system 700 may also include a storage device 720. Examples of astorage device (e.g., storage device 720) include, but are not limitedto, a hard disk drive for reading from and/or writing to a hard disk, amagnetic disk drive for reading from and/or writing to a removablemagnetic disk, an optical disk drive for reading from and/or writing toan optical media (e.g., a CD, a DVD, etc.), a solid-state memory device,and any combinations thereof. Storage device 720 may be connected to bus755 by an appropriate interface (not shown). Example interfaces include,but are not limited to, SCSI, advanced technology attachment (ATA),serial ATA, universal serial bus (USB), IEEE 1394 (FIREWIRE), and anycombinations thereof. In one example, storage device 720 may beremovably interfaced with computer system 700 (e.g., via an externalport connector (not shown)). For instance, the system 700 may include acomputer readable storage media reader 725 and an associatedmachine-readable medium (not illustrated) may provide nonvolatile and/orvolatile storage of machine-readable instructions, data structures,program modules, and/or other data for computer system 700. In oneexample, software 746 may reside, completely or partially, within themachine-readable medium and be accessed via the computer readablestorage media reader 725. In another example, software 746 may reside,completely or partially, within processor 705.

Computer system 700 may also include an input device 710. In oneexample, a user of computer system 700 may enter commands and/or otherinformation into computer system 700 via input device 710. Examples ofan input device 710 include, but are not limited to, an alpha-numericinput device (e.g., a keyboard), a pointing device, a joystick, agamepad, an audio input device (e.g., a microphone, a voice responsesystem, etc.), a cursor control device (e.g., a mouse), a touchpad, anoptical scanner, a video capture device (e.g., a still camera, a videocamera), touch screen, and any combinations thereof. Input device 710may be interfaced to bus 755 via any of a variety of interfaces (notshown) including, but not limited to, a serial interface, a parallelinterface, a game port, a USB interface, a FIREWIRE interface, a directinterface to bus 755, and any combinations thereof. For instance, a usercan enter the constant drive frequency into the optional frequencycontroller 270 via the input device 740.

A user may also input commands and/or other information to computersystem 700 via computer readable storage media reader 725 (e.g., aremovable disk drive, a flash drive, etc.) and/or a communication system730. The communication system 730 may be utilized for connectingcomputer system 700 to one or more of a variety of networks and one ormore remote devices. Examples of a communication system include, but arenot limited to, a network interface card, a modem, and any combinationthereof. Examples of a network or network segment include, but are notlimited to, a wide area network (e.g., the Internet, an enterprisenetwork), a local area network (e.g., a network associated with anoffice, a building, a campus or other relatively small geographicspace), a telephone network, a direct connection between two computingdevices, and any combinations thereof. A network may employ a wiredand/or a wireless mode of communication. In general, any networktopology may be used. Information (e.g., data, software 746, etc.) maybe communicated to and/or from computer system 700 via communicationsystem 730.

Computer system 700 may further include output devices (e.g., a videodisplay adapter) for communicating with peripherals such as a displaydevice. Examples of a display device include, but are not limited to, aliquid crystal display (LCD), a cathode ray tube (CRT), a plasmadisplay, and any combinations thereof. In addition to a display device,the computer system 700 may include one or more other output devices 715including, but not limited to, an audio speaker, a printer, and anycombinations thereof. Such output devices 715 may be connected to bus755 via a peripheral interface. Examples of a peripheral interfaceinclude, but are not limited to, a serial port, a USB connection, aFIREWIRE connection, a parallel connection, and any combinationsthereof. In one example an audio device may provide audio related todata of computer system 700 (e.g., data representing an indicatorrelated to pollution impact and/or pollution offset attributable to aconsumer).

A digitizer (not shown) and an accompanying stylus, if needed, may beincluded in order to digitally capture freehand input. A pen digitizermay be separately configured or coextensive with a display area ofdisplay device. Accordingly, a digitizer may be integrated with displaydevice, or may exist as a separate device overlaying or otherwiseappended to display device.

In conclusion, the present invention provides, among other things, amethod, system, and apparatus for driving an LC circuit at half itsresonant frequency and providing a quasi-sinusoidal current from the LCcircuit for use by an electrosurgical instrument. The quasi-sinusoidalcurrent has less severe current spikes and sparking than those seen inthe prior art. Those skilled in the art can readily recognize thatnumerous variations and substitutions may be made in the invention, itsuse, and its configuration to achieve substantially the same results asachieved by the embodiments described herein. Accordingly, there is nointention to limit the invention to the disclosed exemplary forms. Manyvariations, modifications, and alternative constructions fall within thescope and spirit of the disclosed invention.

What is claimed is:
 1. A method of providing power for anelectrosurgical instrument comprising: generating a non-sinusoidaldriving voltage having a driving frequency; providing the non-sinusoidaldriving voltage to a series LC circuit having a resonant frequencydifferent from the driving frequency, the series LC circuit configuredto present an impedance to limit current; storing energy in the seriesLC circuit during a resonant cycle of the series LC circuit; during theresonant cycle of the series LC circuit, discharging substantially allof the energy stored in the series LC circuit to a power providercomprising a DC bus; and generating a quasi-sinusoidal current in theseries LC circuit from the non-sinusoidal driving voltage.
 2. The methodof claim 1, wherein the limiting current comprises presenting animpedance to the quasi-sinusoidal current in the LC circuit.
 3. Themethod of claim 1, wherein the non-sinusoidal driving voltage is atleast one of a pulsed waveform or a waveform having a square wave shapeand a 50 percent duty cycle.
 4. The method of claim 1, wherein theseries LC circuit has a resonant frequency of substantially twice thesubstantially constant driving frequency.
 5. The method of claim 1,wherein the non-sinusoidal driving voltage is a waveform having a squarewave shape and a 50 percent duty cycle; and the dischargingsubstantially all of the energy stored in the series LC circuitcomprises discharging so that the quasi-sinusoidal current in the seriesLC circuit approaches 0 amperes during a switching of the pulsedwaveform.
 6. The method of claim 5, wherein the waveform has a squarewave shape; and the discharging substantially all of the energy storedin the series LC circuit comprises discharging the energy to the powerprovider during a period of time, the period of time corresponding to asecond half of a resonant cycle of the LC circuit.
 7. The method ofclaim 1, wherein the non-sinusoidal driving voltage is generated by thepower provider.
 8. The method of claim 7, further comprising resupplyingthe substantially all of the energy back to the series LC circuit. 9.The method of claim 1, further comprising resupplying the substantiallyall of the energy back to the series LC circuit.
 10. A power supply foran electrosurgical instrument comprising: a power provider having a DCbus and configured to generate a non-sinusoidal voltage at a drivingfrequency; and a series LC circuit configured to receive thenon-sinusoidal voltage and provide a quasi-sinusoidal current, theseries LC circuit having a resonant frequency that is different from thedriving frequency, the series LC circuit configured to (a) present animpedance to limit current; (b) store energy during a resonant cycle ofthe series LC circuit; (c) during the resonant cycle, dischargesubstantially all of the energy stored in the series LC circuit to thepower provider; and (d) generate a quasi-sinusoidal current from thenon-sinusoidal driving voltage.
 11. The power supply of claim 10,wherein the power provider is configured to generate one of a pulsedwaveform or a waveform having a square wave shape and a 50 percent dutycycle.
 12. The power supply of claim 10, wherein the power providerincludes a power source, an h-bridge, and a buck-boost converterconfigured to provide DC power to the h-bridge; and the DC power has anamplitude configured to control a variable amplitude of the buck-boostconverter.
 13. The power supply of claim 12, wherein the h-bridge isconfigured to receive DC power from the power source, and provide apulsed voltage to the series LC circuit at the driving frequency. 14.The power supply of claim 13, further configured to pass energy from thepower source to the h-bridge and to the series LC circuit during a firsthalf of each pulse of the square wave shape; and pass energy from theseries LC circuit to the h-bridge to the power source during a secondhalf of each pulse of the square wave shape.
 15. The power supply ofclaim 12, wherein the power source comprises a DC bus.
 16. The powersupply of claim 10, wherein the series LC circuit is configured todischarge the substantially all of the energy to the power providerduring a period of time, the period of time corresponding to a secondhalf of a resonant cycle of the LC circuit.
 17. The power supply ofclaim 10, wherein the discharge substantially all of the energy storedin the series LC circuit comprises returning the energy to the powerprovider.
 18. The power supply of claim 17, wherein the power provideris configured to resupply the substantially all of the energy back tothe series LC circuit.
 19. The power supply of claim 10, wherein thepower provider is configured to absorb substantially all energy storedin the series LC circuit during a period of time once per resonant cycleof the series LC circuit and to resupply the substantially all energyback to the series LC circuit.